In general, a lens module of a high-performance digital camera is configured to include an optical lens made of a glass and a lens driving unit for driving the optical lens. In the lens module, a position of the optical lens is adjusted by using the lens driving unit in order to adjust a focus and a magnification ratio of the optical lens.
In this manner, in the conventional high-performance digital camera, since the lens driving unit needs to be installed in order to adjust the focus and magnification, the size of the digital camera is inevitably increased, and it is difficult to miniaturize the high-performance digital camera.
Therefore, recently, a liquid lens capable of adjusting the focus and magnification ratio of the lens without using a lens driving unit has been developed. Due to an electrowetting phenomenon, the focal length of the liquid lens is controlled by adjusting a curvature of a liquid droplet. The principle of the electrowetting is described with reference to FIG. 1. FIG. 1 is a view illustrating a conductive liquid droplet as an example in order to explain the principle of the electrowetting. As illustrated in FIG. 1, if a conductive liquid droplet 40 having a diameter of 2 mm or less is dropped on a top surface of the insulating film 14 which is electrically insulated, a sphere is formed as illustrated by a solid line in FIG. 1. If a voltage is applied between a first electrode 13 disposed under the insulating film 14 and a second electrode 15 interposing the conductive liquid droplet, the electrowetting phenomenon occurs as illustrated by a dotted line in FIG. 1. In other words, if a contact angle between the conductive liquid droplet 40 and the top surface of the insulating film 13 in the state where a voltage is not applied (V=0) is denoted by θ1 and the contact angle in the state where the voltage is applied is denoted by θ2, the formula ‘θ1> θ2’ is satisfied. In this manner, the electrowetting phenomenon denotes a phenomenon where the contact angle is changed when the voltage is applied to the conductive liquid droplet 40 between the first electrode 13 and the second electrode 15. The contact angle is an intrinsic value determined according to characteristics of a liquid droplet, a material such as another liquid or air surrounding the liquid droplet, and a material of the top surface of the insulating film 14. Herein, the diameter of the conductive liquid droplet 40 is limited to 2 mm or less in order to allow the liquid droplet to be predominantly influenced by a surface tension rather than gravity.
FIGS. 2 and 3 are cross-sectional views illustrating conventional liquid lenses. Referring to FIGS. 2 and 3, the focus and magnification of the liquid lens can be adjusted by using the electrowetting phenomenon described above without using a lens driving unit.
In the liquid lens illustrated in FIG. 2, a cylindrical cavity is formed due to vertical side walls, and the conductive liquid droplet 40 and the insulating liquid droplet 50 are contained in the cavity. The liquid lens having a cylindrical cavity described above has an advantage in that the conductive liquid droplet and the insulating liquid droplet contained in the cavity can be stably protected from an external impact. However, the liquid lens has a problem in that it is difficult to inject the conductive liquid droplet and the insulating liquid droplet.
In the liquid lens illustrated in FIG. 3, a truncated conical cavity of which are slanted at an angle of 45° is formed, and the conductive liquid droplet and the insulating liquid droplet are contained in the cavity. In the liquid lens having a truncated conical cavity, it is easy to inject the liquid droplets in comparison with the liquid lens having a cylindrical cavity described above. However, the liquid lens having a truncated conical cavity has a problem in that the liquid droplets contained in the cavity is vulnerable to an external impact in comparison with the liquid lens having a cylindrical cavity.
In addition, a conventional liquid lens is manufactured by using a manufacturing method using a glass or a metal for the container. However, this manufacturing method has a limitation in more precisely manufacturing the cavity of the container.